The present invention relates to a method of preparing (trifluoromethyl)pyridine compounds and more in particular to a method of preparing chlorinated (trifluoromethyl)pyridine compounds.
Fluorination of (trichloromethyl)pyridine compounds has been carried out by vapor phase fluorination which requires the use of high temperatures. Such vapor phase reactions suffer from disadvantages including, for example, energy costs associated with elevating the temperature of the reactants. Additionally, at the temperature necessary for the vapor phase fluorination reaction, both the starting materials and the end products can be decomposed or converted into undesirable by-products which lead to low conversions and low selectivities to the desired (trifluoromethyl)pyridine products. See, for example, U.S. Pat. Nos. 4,266,064 and 4,288,599.
Another method of preparing (trifluoromethyl)pyridine compounds has been to contact a (trichloromethyl)pyridine compound with antimony trifluorodichloride (SbF.sub.3 Cl.sub.2). See, for example, U.S. Pat. Nos. 3,136,822; 3,787,420; and 3,818,019. The disadvantages associated with this reaction are, for example, the difficulty in controlling an extremely exothermic reaction, the high cost of antimony trifluorodichloride and the difficulty in recycling the antimony by-product. Thus, it is evident that a more efficient and economical method of preparing (trifluoromethyl)pyridine compounds is desirable.
In U.S. Pat. No. 4,184,041 it is disclosed that (trichloromethyl)pyridines are converted to (trifluoromethyl)pyridines employing HF (at 0.degree.-50.degree. C.) or metal fluorides (SbF.sub.3 at 100.degree.-250.degree. C.) as fluorinating agents.
In U.S. Pat. No. 4,259,496, a method is taught for the side-chain fluorination of 3-methylpyridine. In this method, 3-methylpyridine is reacted with HF and chlorine in the liquid phase at an elevated temperature and superatmospheric pressure resulting in the formation of 3-(trifluoromethyl)pyridine, a 3-(dichlorofluoromethyl)pyridine, 3-(difluorochloromethyl)pyridine or derivatives thereof containing one or more chlorine or fluorine atoms as substituents in the pyridine ring.
The present invention differs from the prior known methods of preparing (trifluoromethyl)pyridine compounds by employing superatmospheric pressures when reacting optionally chlorinated (trichloromethyl)-pyridines with HF in the presence of a catalyst whereby the desired (trifluoromethyl)pyridine compounds are produced in a more efficient manner when compared to a non-pressurized reactions.